Endocardial dispersive electrode for use with a monopolar RF ablation pen

ABSTRACT

Methods and devices for forming a lesion in a target tissue having a cavity within. A first RF electrode and a second RF electrode can be coupled to opposite poles of an RF current source. The second electrode can be inserted into the tissue cavity and expanded to contact the target tissue from within. The first electrode can be externally disposed against the target tissue while applying RF current between the first and second electrodes to ablate the target tissue. Some methods are directed to ablating tribiculated atrial wall tissue to treat atrial fibrillation. The second electrode can contact the tribiculated tissue directly from within to provide a direct path between the two electrodes. In some methods, the second electrode is inserted through an incision made to remove an atrial appendage. The methods can provide deeper, narrower lesions relative to those made using remote, indifferent electrodes. Atrial fibrillation ablation procedures can be performed using the invention, requiring fewer incisions than conventional methods.

FIELD OF THE INVENTION

The present invention relates generally to devices for cardiac surgery,and more specifically to devices for ablation of cardiac tissue.

BACKGROUND OF THE INVENTION

The present invention is directed toward treatment of tachyarrhythmias,which are heart rhythms in which one or more chambers of the heartexhibit an excessively fast rhythm. In particular, the present inventionis directed toward treatment of tachycardias, which are due to thepresence of ectopic foci within the cardiac tissue or due to thepresence of aberrant condition pathways within the cardiac tissue.

There are many medical treatments that involve instances of cutting,ablating, coagulating, destroying, or otherwise changing thephysiological properties of tissue. These techniques can be usedbeneficially to change the electrophysiological properties of tissue.For example, ablation of cardiac tissue can be used to cure variouscardiac conditions. Normal sinus rhythm of the heart begins with thesinoatrial node (or “SA node”) generating a depolarization wave front.The impulse causes adjacent myocardial tissue cells in the atria todepolarize, which in turn causes adjacent myocardial tissue cells todepolarize. The depolarization propagates across the atria, causing theatria to contract and empty blood from the atria into the ventricles.The impulse is next delivered via the atrioventricular node (or “AVnode”) and the bundle of HIS (or “HIS bundle”) to myocardial tissuecells of the ventricles. The depolarization of these cells propagatesacross the ventricles, causing the ventricles to contract. Thisconduction system results in the described, organized sequence ofmyocardial contraction leading to a normal heartbeat.

Sometimes aberrant conductive pathways develop in heart tissue, whichdisrupt the normal path of depolarization events. For example,anatomical obstacles in the atria or ventricles can disrupt the normalpropagation of electrical impulses. These anatomical obstacles (called“conduction blocks”) can cause the electrical impulse to degenerate intoseveral circular wavelets that circulate about the obstacles. Thesewavelets, called “reentry circuits,” disrupt the normal activation ofthe atria or ventricles.

The aberrant conductive pathways create abnormal, irregular, andsometimes life-threatening heart rhythms, called arrhythmias. Anarrhythmia can take place in the atria, for example, as in atrialtachycardia, atrial fibrillation or atrial flutter. The arrhythmia canalso take place in the ventricle, for example, as in ventriculartachycardia.

The lesions used to treat atrial fibrillation, are typically long andthin and are carefully placed to interrupt the conduction routes of themost common reentry circuits. More specifically, the long thin lesionsare used to create a maze pattern that creates a convoluted path forelectrical propagation within the left and right atria. The lesionsdirect the electrical impulse from the SA node along a specified routethrough all regions of both atria, causing uniform contraction requiredfor normal atrial transport function. The lesions finally direct theimpulse to the AV node to activate the ventricles, restoring normalatrioventricular synchrony. Several surgical approaches have beendeveloped with the intention of treating atrial fibrillation. Oneparticular example is known as the “maze procedure,” as is disclosed byCox, J L et al. in “The surgical treatment of atrial fibrillation. I.Summary” Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991);and also by Cox, J L in “The surgical treatment of atrial fibrillation.IV. Surgical Technique”, Thoracic and Cardiovascular Surgery 101(4), pp.584-592 (1991), both of which are incorporated by reference herein intheir entireties. In general, the “maze” procedure is designed torelieve atrial arrhythmia by restoring effective atrial systole andsinus node control through a prescribed pattern of incisions about thetissue wall. In the early clinical experiences reported, the “maze”procedure included surgical incisions in both the right and the leftatrial chambers. However, more recent reports predict that the surgical“maze” procedure may be substantially efficacious when performed only inthe left atrium, such as is disclosed in Sueda et al., “Simple LeftAtrial Procedure for Chronic Atrial Fibrillation Associated With MitralValve Disease” (1996), which is incorporated herein by reference in itsentirety.

When modifying the electrophysiological properties of cardiac tissue byablation, or by other means of destroying tissue to create lesions,physicians must carefully place the lesions. Otherwise, tissue will beunnecessarily destroyed. In addition, the heart is in close proximity tonerves and other nervous tissue and the destruction of this tissue willresult in severe harm to the patient. Anatomical methods are used tolocate the areas to be ablated or otherwise modified. In other words,the physician locates key structures such as the mitral valve annulusand the pulmonary veins. Lesions are typically formed that blockpropagations near these structures. Additional lesions are then formedwhich connect these lesions and complete the so-called “maze pattern.”However, the exact lesion pattern, and number of lesions created, canvary from patient to patient.

The surgical “maze procedure” as performed in the left atrium generallyincludes forming vertical incisions from the two superior pulmonaryveins and terminating in the region of the mitral valve annulus,traversing the inferior pulmonary veins en route. An additionalhorizontal line also connects the superior ends of the two verticalincisions. Thus, the atrial wall region bordered by the pulmonary veinostia is isolated from the other atrial tissue. In this process, themechanical sectioning of atrial tissue eliminates the precipitatingconduction to the atrial arrhythmia by creating conduction blocks withinthe aberrant electrical conduction pathways.

Injection of alcohol into heart tissue has also been employed to ablatecardiac tissue. Alcohol may be delivered to blood vessels supplying thetissue to be ablated, as described in “Transcoronary Chemical Ablationof Arrhythmias”, by Nellens et al, Pace Vol. 15, pages 1368-1373,September 1992. Alternatively, alcohol can be delivered directly to thetissue to be ablated by means of a needle inserted through a catheter,as described in “Chemical Ablation by Subendocardial Injection ofEthanol via Catheter—Preliminary Results in the Pig Heart”, byWeismuller et al, European Heart Journal, Volume 12, pages 1234-1239,1991.

Although successful at treating AF, the surgical maze procedure is quitecomplex and is currently performed by only a few skilled cardiacsurgeons in conjunction with other open-heart procedures. Tools thatcould reliably duplicate the Maze incisions by other means (e.g. radiofrequency, laser, microwave, ultrasound energy) will reduce the time andinvasiveness required for the maze procedure and make it more accessibleto more surgeons. Problems faced by these methods, however, include (a)the creation of continuous, linear lesions in the atria for theprevention of atrial fibrillation, (b) minimization of clotting andthromboembolism, (c) the effect of heat loss due to circulating blood,(d) minimization of lesion width and minimization of atrial debulking,(e) conforming to an irregular myocardial thickness, (f) adaptability toa variety of lesion geometries and (g) usefulness from either theendocardial surface of an open heart, or the epicardial surface of abeating heart.

One particular procedure, the monopolar RF ablation of cardiac atrialtissue to treat atrial fibrillation, causes wide, shallow lesions, dueto current dispersion through the tissue. In heavily tribiculatedtissue, monopolar ablation is only feasible endocardially. An epicardialapproach using conventional methods will not efficiently transfer energyinto the deep tissue folds, due to that tissue being out of theconductive path between the external epicardial electrode and the remoteindifferent electrode. Bipolar hemostats have been used to concentratethe current through a direct tissue path between closely spacedelectrodes to provide improved ablation through smooth or heavilytribiculated tissue. However, the bipolar hemostats require significanttissue cutting to provide complete access to necessary lesion sites.

Some tissue cutting is required in a Maze procedure. In particular, theatrial appendages are typically removed. Monopolar RF cardiac ablationrequires significant additional tissue cutting in order to position theelectrode in the proper positions to perform endocardial ablations.

What would be desirable are methods that would reduce tissue cutting andimprove the efficacy of epicardial ablation. What would be advantageousare devices that direct RF current along the desired transmural path,creating narrower and deeper lesions.

SUMMARY OF THE INVENTION

The present invention includes devices and methods for ablation ofcardiac tissue in which a hand-held, monopolar RF ablation device isused to ablate cardiac tissue in conjunction with an expandableendocardial electrode inserted into a heart chamber and urged againstthe chamber wall. The endocardial electrode can be expandable orinflatable and have a conductive surface. The endocardial electrode maybe inserted through a small incision made in the heart chamber walland/or through the opening made by the removal of the atrial appendage.The electrode can then be expanded or inflated, urging the conductivesurface against the endocardium.

A monopolar RF ablation device can then be drawn along the desiredlesion line on the epicardium. A current path is thus formed between theepicardial RF device and the expanded surface electrode disposed againstthe endocardium. The direct path between the external monopolar RFelectrode and the endocardial surface internal electrode can provide anarrower, deeper lesion relative to the lesion created using a currentpath between the RF electrode and an external, indifferent electrode.The incision required to insert the expandable or inflatable electrodecan be significantly smaller than that required to insert andsuccessfully maneuver the monopolar RF electrode endocardially.

The monopolar electrode tissue-contacting surface can be connected toone pole of a radio frequency generator while the other pole of thegenerator is connected to a large surface, endocardial electrode. In oneembodiment of the invention, the epicardial monopolar electrode is aconventional radio frequency ablation device such as the Cardioblate®pen available Medtronic, Inc.

The present invention includes methods for forming a lesion in a targettissue having a cavity within. The methods can include providing a firstRF electrode coupled to a RF current source and a second RF electrodeelectrically coupled to form a ground path for the first RF electrode,wherein the second RF electrode is electrically conductive andexpandable, wherein the second electrode has a first, unexpandedconfiguration and a second, expanded configuration. The second electrodecan be inserted into the tissue cavity and expanded to the secondconfiguration to contact the target tissue from within the cavity. Thefirst electrode can be disposed against the target tissue while applyingRF current between the first and second electrodes to ablate the targettissue.

The present invention includes methods for treating atrial fibrillationthat do not require making any incisions in the right or left atriaother than those to remove the left and/or right atrial appendages. Themethods can include making lesion paths of the Maze, Maze 3 or ModifiedMaze 3 procedures, while performing only the incisions to remove theatrial appendages. The methods can include making lesions along thepaths described in the: Cox, J L et al.; Cox, J L; and Sueda et al.publications, previously incorporated by reference in the presentapplication.

In one method, an incision is made to remove the right atrial appendageand the method does not include making any other incisions in the rightatrium. One such method does not include making an incision from theright atrial appendage incision toward the inferior vena caval orifice.Another such method does not include making a posterior longitudinalincision starting caudal to the superior caval cannulation site at thedorsal aspect of the right atrium.

In another method, an incision is made to remove the left atrialappendage, and the method does not include making any other incisions inthe left atrium. One such method does not include making a standardatriotomy in the inter-atrial groove between the left and right atria.

One device includes a shaft and an electrode including an envelopehaving an interior and an electrically conductive flexible surfacedisposed near the shaft distal region. The second electrode surface canhave a first configuration having a first interior volume within theconductive surface and a second, expanded configuration having a secondinterior volume within the conductive surface, with the second volumebeing greater than the first volume.

In some devices, the electrically conductive surface includes an outermetallic layer disposed over a polymeric layer. Some electrodes includean outer metallic mesh disposed over a polymeric layer. The polymericlayer can be substantially resistant to fluid permeation, such that thepolymeric layer is inflatable. The envelope can be formed of anelectrically conductive polymer. Some envelopes according to the presentinvention are porous, and the electrically conductive surface can be theouter surface an electrically conductive porous mesh. Some meshes aremetallic meshes.

Some device embodiments have a fluid lumen extending through the shaft,which can be used to inflate the envelope. Other embodiments haveenvelopes biased to expand when unconstrained. Still other embodimentenvelopes include shape memory materials that expand when heated to bodytemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art, fragmentary, cross-sectional view of a heartchamber wall having tribiculated tissue, the wall being partiallyablated using an external RF electrode and a remote, indifferentelectrode;

FIG. 2 is a fragmentary, cross-sectional view of the tribiculated heartchamber wall of FIG. 1, being ablated using the RF electrode of FIG. 1and an internal, expandable surface electrode contacting thetribiculated tissue;

FIG. 3 is a diagrammatic, longitudinal cross-sectional view of onedevice having an expandable surface electrode, shown in an un-expandedconfiguration;

FIG. 4 is a diagrammatic, longitudinal cross-sectional view of anotherdevice having an expandable surface electrode, shown in an un-expandedconfiguration;

FIG. 5 is a diagrammatic, longitudinal cross-sectional view of yetanother device having an expandable surface electrode, shown in anun-expanded configuration within a retractable delivery sheath;

FIG. 6 is a diagrammatic, longitudinal cross-sectional view of stillanother device having an expandable surface electrode, shown in anun-expanded configuration within a retractable delivery sheath;

FIG. 7 is a diagrammatic, longitudinal cross-sectional view of a devicehaving an expandable surface electrode, shown in an expandedconfiguration;

FIG. 8 is a fragmentary, cross-sectional view of an envelope formed ofan electrically conductive material;

FIG. 9 is a fragmentary, cross-sectional view of an envelope formed ofan electrically conductive material layer formed over another, moreinterior material;

FIG. 10 is a fragmentary, cross-sectional view of an envelope formed ofan electrically conductive mesh formed over another, more interiormaterial; and

FIG. 11 is a fragmentary, side view of an envelope formed of anelectrically conductive porous mesh.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a prior art method for ablating cardiac tissue in theatria. In particular, a tribiculated region of the atria is illustrated.An atrial region 30 is illustrated, having an atrial wall 32, aninterior 34, and tribiculated tissue 36 is illustrated, having gaps orcavities 37 disposed between the tribiculated tissue regions. Amonopolar electrode 40 is illustrated, coupled to an RF energy source42. A lesion area 38 formed from the ablation is also illustrated. InFIG. 1, a remote, indifferent electrode (not illustrated in FIG. 1)provides the return path for the RF energy supplied by monopolarelectrode 40. As may be seen from inspection of FIG. 1, lesion area 38is fairly wide, and does not penetrate into tribiculated tissue regions36. The shallow and insufficiently deep lesions are formed due to the RFcurrent dispersion, indicated at 44, as RF energy takes a path to theindifferent electrode that does not include penetrating directly intoatrial wall 32. As maybe seen from inspection of FIG. 1, monopolarablation of some tissue regions may not be feasible using a monopolarelectrode, due to the shallow penetration. In such cases, endocardialablation, using electrode 40, may be required.

FIG. 2 illustrates atrial region 30 of FIG. 1, using devices and methodsaccording to the present invention. Tribiculated tissue regions 36 maybe seen, as discussed with respect to FIG. 1. In FIG. 2 however, asecond electrode 46 may be seen, having an envelope surface 48contacting the tissue of atrial wall 32 and tribiculated tissue regions36. Second electrode 46 may be described as an envelope or membrane, invarious embodiments. Second electrode 46 may be seen to contacttribiculated tissue 36 and other endocardial tissue directly, providinga short, direct current path, indicated at 50, between second electrode46 and a monopolar electrode 40. As a result of the more direct currentpath, a deeper and narrower lesion 52 may be formed between monopolarelectrode 40 and second electrode 46. As illustrated in FIG. 2, thepresent invention can provide a lesion formed entirely through the heartchamber wall, using an external electrode and the second, internalelectrode.

FIG. 3 illustrates a device 70 that can be used to facilitate ablatingcardiac tissue. Device 70 includes a device shaft 72 having an interior84, a proximal region 74, and a distal region 76. An expandable envelope78 may be seen affixed to shaft distal region 76. Envelope 78 is shownin a first, unexpanded configuration, having folds 80 and an internalvolume, indicated at 82. Envelope 78 further includes a proximal mouth77, secured to shaft distal region 77. As used herein, “expandable”refers to the envelope having an unexpanded and an expandedconfiguration, wherein the expanded configuration has a larger internalvolume than the first configuration. The term “expandable” does notrequire that the envelope be elastic or stretchable in any way.

While some embodiments include a proximal shaft, other embodiments haveno shaft. Some embodiments utilize the proximal mouth of the envelope orballoon to expand or inflate the envelope or balloon. In suchembodiments, the balloon or envelope can be inserted into the heartchamber through an opening and inflated through a fluid supplied to theballoon proximal mouth.

Shaft 72 may be solid in some embodiments and hollow in otherembodiments, carrying an inflation lumen within. In some embodiments,shaft 72 has a length of between about 12 and 18 inches. Someembodiments have a shaft length less than 12 inches, while otherembodiments have a shaft length less than 6 inches. Some shafts have anouter diameter of between about 20 Fr. and 30 Fr. Shaft 72, and othershafts according to the present invention may be of shaft or tubematerials well known to those skilled in the biomedical arts. Exemplaryshaft materials include silicone, PEBAX, polyurethane, and PVC.

FIG. 4 illustrates another device 90 that can be used according to thepresent invention. Device 90 includes a shaft 92 having a proximalregion 94 and a distal region 96. Shaft 92 further includes a lumen 100within, carrying a proximal push rod 102 having a distal flange 104attached to the push rod. An envelope 98 may be seen, in an unexpandedconfiguration within shaft lumen 100. In use, push rod 102 can be usedto force envelope 98 out of shaft 92, allowing envelope 98 to expand.Envelope 98 may be self-expanding in some embodiments, and require fluidinflation, in other embodiments.

FIG. 5 illustrates still another device 120 having a shaft 128 having anenvelope 132 secured to a shaft distal region 129. Envelope 132 may beseen to be in an unexpanded configuration. Envelope 132 may be seen tobe in a compressed, folded state. Device 120 further includes an outerdelivery sheath or sleeve 134 having a distal region 124 and a proximalregion 126. Sleeve 134 can be proximally retracted from shaft 128bearing envelope 132, or shaft 128 and envelope 132 can be distallyurged out of delivery sleeve 134. In some embodiments, envelope 132 isself-expanding. In other embodiments, envelope 132 is inflated withfluid supplied through a lumen extending through shaft 128.

FIG. 6 illustrates still another device 140 having a delivery sheath 142having distal region 144 and proximal region 146. An expandable envelope150 may be seen, secured to a shaft 148. Shaft 148 and envelope 150 areboth disposed within delivery sheath 142. In some embodiments, envelope150 is biased to expand radially outward to form a spherical or bulbousshape, when unconstrained by outer sheath 142. In some embodiments, theenvelope, for example, envelope 150, may be urged distally from aconstraining tube, for example, sheath 142. After being distally urgedfrom the outer tube, the envelope may be radially expanded and the outertube used as a catheter to guide the now expanded envelope to the targetsite.

FIG. 7 illustrates device 70 of FIG. 3, in a second, expandedconfiguration. Device 70 may be seen to have a much larger envelopeinternal volume 82. Envelope 78 may be seen to be in a significantlyexpanded configuration relative to that seen in FIG. 3. In someembodiments, envelope 78 is self-expanding. In other embodiments,envelope 78 is inflated with fluid provided through a lumen providedthrough shaft 72, within shaft interior 84. In some methods, saline isused as the inflation fluid.

FIG. 8 illustrates a section of envelope material 160, wherein theentire thickness of the envelope material is electrically conductive.One such envelope material includes a conductive polymer.

FIG. 9 illustrates another envelope 162. Envelope 162 includes an innerlayer 164 and an outer layer 166. In some embodiments, inner layer 164is a polymeric, substantially nonconductive material. Outer layer 166can be an electrically conductive material, for example, a metallicfilm. In some embodiments, envelope 162 is formed of Mylar, having ametallic film disposed over a polymeric layer.

FIG. 10 illustrates yet another envelope section 168 having an inner,substantially contiguous layer 170 and an outer mesh 172. In someembodiments, inner layer 170 is a polymeric layer that is substantiallyimpervious to fluid flow, enabling the envelope to be fluid expanded. Insome envelopes, mesh 172 is an electrically conductive, metallic mesh.Mesh 172 can be formed of Nitinol in some embodiments and stainlesssteel in other embodiments. In still other embodiments, electricallyconductive mesh 172 is formed of an electrically conductive polymer. Insome envelopes, mesh 172 is formed of a material biased to expandoutwardly when unconstrained. In other embodiments, mesh 172 is formedof a shape memory material, set to expand outwardly when heated towardbody temperature from room temperature. For the purposes of the presentinvention, room temperature may be defined as about 70 degreesFahrenheit.

FIG. 11 illustrates still another envelope section 174, having a porousmesh including braids or strands 176 having pores 178 disposedtherebetween. In embodiments having a porous mesh, the mesh itself maybe self-expandable or may be expanded through an inflation envelopedisposed within the mesh.

In one method according to the present invention, a first RF electrodeis provided, coupled to a RF current source. A second RF electrode isalso provided and coupled to form a ground path for the first RFelectrode. The second electrode can include an electrically conductiveenvelope surface defining an interior volume within. The envelope canhave a first, unexpanded configuration and a second, expandedconfiguration. The second configuration can have an interior volumegreater than the first, unexpanded configuration. An incision can bemade in a heart chamber wall. A preferred use of the present inventionis to ablate atrial wall tissue. One such incision is an incision madeto remove an atrial appendage. Such incisions are typically made as partof a maze procedure.

After the incision is made, the second electrode can be inserted throughthe incision and into the heart chamber interior. The second electrodecan then be expanded to urge the second electrode conductive surface tocontact a target region of the heart chamber endocardium. The firstelectrode can be disposed against the target region epicardium whileapplying RF current through the first electrode.

A short, direct current path is thus formed between the first electrodeon the epicardium and the expanded surface electrode bearing against theendocardium. The second electrode can be urged against tribiculatedtissue to provide direct contact with the second electrode and thereforeprovide a short and direct current path directed through thetribiculated tissue. A lesion resulting from the current path formedbetween the first electrode and the second, interior electrode, can thusbe both deeper and narrower than lesions formed using the externalelectrode and a remote indifferent electrode.

In some methods, the second electrode is biased to expand whenunconstrained, and is freed from constraint after being inserted intothe heart chamber through the incision. In some such methods, a sleeveor delivery tube is retracted from about the constrained secondelectrode. While some electrodes are simply biased to expand outwardwhen unconstrained, other internal electrodes are formed of a shapememory material that expands when heated toward body temperature.

Some methods include providing a fluid expandable or inflatableenvelope. In such methods, a fluid, for example, saline, can be injectedinto the envelope interior to expand the envelope to its fully expandedshape.

Applicant believes that the present invention provides novel methods forforming lesions entirely through the atrial wall using a first, externalelectrode on the epicardium and a second, expanded surface internalelectrode on the endocardium, simultaneously. This may be contrastedwith using an electrode drawn over the endocardial surface, for example,a pen electrode. While forming a lesion using an inserted pen electrodemay be efficacious, a large incision must be made through the heartchamber wall in order to properly direct the drawing of the penelectrode across the endocardium. Using the present invention, anincision only large enough to insert the expandable or inflatableenvelope need be made.

Applicant believes that target sites in the entire right and left atrialfree wall regions may be ablated using RF ablation, and entirely throughthe atrial wall, where ablating these sites does not require making anincision in the right atrium from the excised atrial appendage parallelto the right atrioventricular groove toward the inferior vena cava(IVC), an incision from about 1 cm, above the IVC cannulation site tothe top of the atrioventricular groove, or in the left atrium in theinteratrial groove.

In general, the present invention provides methods for forming lesionsin target tissue having a cavity within. In the general case of theinvention, a first electrode is coupled to a RF current source and asecond RF electrode is electrically coupled to form a ground path forthe first RF electrode. The second electrode can be inserted into thetissue cavity and expanded to contact the target tissue from within thecavity. The first electrode can then be disposed against the targettissue from the outside, while applying RF current through the firstelectrode to ablate the target tissue.

It will be appreciated by those skilled in the art that while theinvention has been described above in connection with particularembodiments and examples, the invention is not necessarily so limited,and that numerous other embodiments, examples, uses, modifications anddepartures from the embodiments, examples and uses are intended to beencompassed by the claims attached hereto. The entire disclosure of eachpatent and publication cited herein is incorporated by reference, as ifeach such patent or publication were individually incorporated byreference herein.

1. A method for forming a lesion in cardiac tissue, the methodcomprising: providing a first RF electrode coupled to a RF currentsource; providing a second RF electrode electrically coupled to form acurrent path for the first RF electrode, wherein the second RF electrodeincludes an electrically conductive envelope surface defining aninterior volume within, wherein the envelope has a first, unexpandedconfiguration and a second, expanded configuration, wherein the secondconfiguration has an interior volume greater that the firstconfiguration interior volume; making an incision in a heart chamberwall; inserting the second electrode through the incision and into theheart chamber interior; expanding the second electrode conductivesurface to the second configuration to contact a target region of theheart chamber endocardium; and disposing the first electrode against thetarget region epicardium while applying RF current between the first andsecond electrodes.
 2. A method as in claim 1, wherein the secondelectrode is biased to expand when unconstrained, and wherein theexpanding step includes allowing the second electrode to expand insidethe heart chamber.
 3. A method as in claim 1, wherein the secondelectrode includes a shape memory material that expands when heated tobody temperature, and wherein the expanding step includes allowing thesecond electrode to expand inside the heart chamber.
 4. A method as inclaim 1, further comprising providing a sheath over the envelope in thefirst, unexpanded envelope configuration, and retracting the sheathrelative to the envelope.
 5. A method as in claim 1, wherein the secondelectrode is fluid inflatable, and wherein the expanding step includesinjecting fluid into the second electrode interior to expand the secondelectrode inside the heart chamber.
 6. A method as in claim 1, whereinthe making incision includes making an incision to remove an atrialappendage.
 7. A method as in claim 1, wherein making the incisionincludes amputating the right atrial appendage.
 8. A method as in claim7, wherein inserting the second electrode through the incision includesinserting the second electrode through the incision amputating the rightatrial appendage.
 9. A method as in claim 8, wherein the target regionincludes a region disposed between the middle of the anterolateralaspect of the incision amputating the right atrial appendage and theinferior vena caval orifice.
 10. A method as in claim 9, furthercomprising making a second lesion that is slightly curved and extendsalong the border of the inter-atrial septum and ends at theatrioventricular groove, where the second lesion is formed by applyingRF current between the first and second electrodes, where the secondelectrode has been inserted through the incision amputating the rightatrial appendage.
 11. A method as in claim 8, wherein the lesion isformed using the first and second electrodes, from the middle of theanterolateral aspect of the incision amputating the right atrialappendage towards the inferior vena caval orifice.
 12. A method forforming a lesion in cardiac tissue, the method comprising: providing afirst RF electrode coupled to a RF current source; providing a second RFelectrode electrically coupled to form a current path for the first RFelectrode, wherein the second RF electrode includes an electricallyconductive envelope surface defining an interior volume within, whereinthe envelope has a first, unexpanded configuration and a second,expanded configuration, wherein the second configuration has an interiorvolume greater that the first configuration interior volume; making anincision in a heart chamber wall; inserting the second electrode throughthe incision and into the heart chamber interior; expanding the secondelectrode conductive surface to the second configuration to contact atarget region of the heart chamber endocardium; disposing the firstelectrode against the target region epicardium while applying RF currentbetween the first and second electrodes; and wherein making the incisionincludes amputating the left atrial appendage.
 13. A method as in claim12, wherein inserting the second electrode through the incision includesinserting the second electrode through the incision amputating the leftatrial appendage.
 14. A method as in claim 13, wherein the target regionincludes a region disposed within the inter-atrial groove between theleft and right atria.
 15. A method as in claim 14, wherein the lesion isformed by applying RF current between the first and second electrodes.16. A method for performing a maze procedure to treat atrialfibrillation by ablating atrial tissue to form at least one lesion inthe atrial tissue, the method comprising: providing a first RF electrodecoupled to one pole of an RF current source; providing a second RFelectrode electrically coupled to the other pole of the RF currentsource; inserting the second electrode into the atrial chamber;disposing the first electrode against the target tissue and drawingpaths with the first electrode to form the maze lesions while applyingRF current between the first and second electrodes to ablate the targettissue in a maze pattern, wherein the inserting is done through anincision made at the atrial appendage; and wherein the incision is madeto remove the left atrial appendage, and wherein the method does notinclude making any other incisions in the left atrium.
 17. A method forperforming a maze procedure to treat atrial fibrillation by ablatingatrial tissue to form at least one lesion in the atrial tissue, themethod comprising: providing a first RF electrode coupled to one pole ofan RF current source; providing a second RF electrode electricallycoupled to the other pole of the RF current source; inserting the secondelectrode into the atrial chamber; disposing the first electrode againstthe target tissue and drawing paths with the first electrode to form themaze lesions while applying RF current between the first and secondelectrodes to ablate the target tissue in a maze pattern, wherein theinserting is done through an incision made at the atrial appendage; andwherein the incision is made to remove the left atrial appendage,wherein the method does not include making an atriotomy in theinter-atrial groove between the left and right atria.